1. Field of the Invention
This invention relates to the measurement of magnetic fields. More specifically, this invention relates to the measurement of electrical characteristics of geological formations from within steel cased wells using magnetic circuits.
2. Description of Related Art
Recently the U.S. Department of Energy has sought research proposals on the development of technology to measure the magnetic fields that are outside a steel well casing from inside the steel well casing. A number of partial solutions have been proposed. Generally, these approaches have important limitations, these limitations include: the need for magnetically saturating the well casings, operating only within a few dozen hertz, relying on electromagnetic effects the saturation of the magnetic well casing, a magnetic focusing device, and passing an electromagnetic signal through a conductor, and do not address the use of magnetic sensors suitable for the measurement of the effects of magnetic signals with frequencies above 2 k Hz. Prior approaches also are limited by the electrical skin depth of the conductor, thus as the frequency increases the signal strength decreases. Nor do they use magnetic circuits to direct the magnetic flux directly to the magnetic sensor. Nevertheless, the reader is referred to the following U.S. patent documents for general background material. Each of these patents is hereby incorporated by reference in its entirety for the material contained therein.
U.S. Pat. No. 3,980,881 describes a well logging system of the type utilizing a single conductor cable to provide power from the surface equipment to a down hole subsurface unit and for simultaneously supplying current mode telemetry signals from one or more radiation detectors in the subsurface unit to the surface equipment.
U.S. Pat. No. 3,982,176 describes a well logging system that simultaneously employs a conventional deep induction log and a radio frequency dielectric log to differentiate similar high resistivity fresh water and oil prospective zones.
U.S. Pat. No. 4,071,815 describes a borehole tool for logging the remnant magnetic field of the earth formations surrounding a borehole that includes a coil system having a transmitter, receiver, and nulling coils, a phase-sensitive detector connected across the receiver and nulling coils and a detector system having a pair of axially spaced magnetometers, a pair of counters, an oscillator, a comparator, and a transmitter.
U.S. Pat. No. 4,100,483 describes a dielectric well logging system that includes a logging tool adapted to be passed through a borehole traversing an earth formation.
U.S. Pat. No. 4,110,682 describes a well logging apparatus that uses a narrow wall-engaging pad equipped with an array of vertical electrodes.
U.S. Pat. No. 4,117,394 describes a well logging apparatus that uses a narrow wall-engaging pad equipped with an array of long vertical electrodes.
U.S. Pat. No. 4,130,793 describes a dielectric well logging means that utilizes the signals from a pair of receivers for providing clock pulses corresponding to earth formation dielectric constant.
U.S. Pat. No. 4,205,288 describes an electrical transformer having an electrical winding and a magnetic core having two parallel magnetic circuits having unequal mean lengths.
U.S. Pat. No. 4,319,191 describes a dielectric well logging system that has its coils aligned radially, rather than in alignment, with respect to the longitudinal axis of a sonde, which moves a coil through a borehole.
U.S. Pat. No. 4,320,340 describes a well logging method and apparatus that measures the density of the flux field established inside the casing due to galvanic current flow longitudinally within the casing.
U.S. Pat. No. 4,323,848 describes a method of well logging in petroleum exploration, where a magnetometer is disposed in a well bore to provide indications of the distribution, filimentation, and distortion of a controlled current flow within adjoining strata of interest.
U.S. Pat. No. 4,334,205 describes an electromagnetic device that comprises an annular armature, an inner stator structure defining outwardly extending pole pieces and an outer stator structure defining inwardly extending pole pieces.
U.S. Pat. No. 4,359,687 describes an apparatus for borehole measurements of the induced polarization of earth formations.
U.S. Pat. No. 4,361,808 describes methods and systems for measuring the dielectric constant of an earth formation.
U.S. Pat. No. 4,435,977 describes a method of identifying potential low water cut hydrocarbon producing zones in a sand or sandstone formation by logging the formation to determine its permeability and porosity values and generating from said two sets of values a log of specific surface areas of the formation.
U.S. Pat. No. 4,456,898 describes thermal compensators that comprise at least one metallic alloy in amorphous form, which are especially useful in stabilizing magnetic devices under conditions of changing ambient operating temperature.
U.S. Pat. No. 4,499,422 describes a digital induction resistivity-logging tool for digitally measuring both the in-phase and the quadrature phase components in a receiver signal generated in response to induce eddy currents flowing in the earth""s sub-surface formations.
U.S. Pat. No. 4,502,010 describes a method of well logging in petroleum exploration and apparatus for use in the method.
U.S. Pat. No. 4,524,272 describes a method for measuring the location, linear.
flow rate and volume flow rate of undesired water flow behind well casing in a well, that includes irradiating borehole environs with high energy neutrons from a neutron source located in a well tool in the borehole.
U.S. Pat. No. 4,528,508 describes a method and apparatus, which allows remote sensing and in-situ volumetric measurement of liquid petroleum reserves.
U.S. Pat. No. 4,553,097 describes a well logging apparatus and method which can be used as a wireline logging device or technique, and is also suitable for being employed in a logging-while-drilling device.
U.S. Pat. No. 4,560,663 describes a well logging method for identifying the presence of crude petroleum within subsurface earth formations by detecting electron spin resonance signals along a well bore and identifying crude petroleum as the source of those signals by enhancing and/or suppressing the signal by the presence of a chemical.
U.S. Pat. No. 4,609,873 describes a dielectric well logging system that determines dielectric constant and resistivity in formations invaded by water to determine oil and water saturation of the formations.
U.S. Pat. No. 4,631,604 describes a magnetic circuit that is biased by applying signals having noise-like properties to the magnetic circuit.
U.S. Pat. No. 4,652,828 describes well logging techniques for obtaining improved measurements of formation dielectric permitivity, conductivity, and water-filled porosity.
U.S. Pat. Nos. 4,656,422 and 4,792,757 describe oil well logging tools, which make use of nucleons, which are chemically bound to oil and water in geological formations that possess magnetic moments, which align in the earth""s magnetic field causing the natural nuclear paramagnetism of the formation.
U.S. Pat. No. 4,692,706 describes a method and apparatus for determining the water saturation of a petroleum reservoir earth formation that includes transmitting electromagnetic energy in the earth formation from within a borehole traversing the earth formation and at least two frequencies within a preferred range of frequencies.
U.S. Pat. No. 4,697,150 describes a well logging instrument for measuring the resistivity of relatively thin formation beds.
U.S. Pat. No. 4,748,415 describes methods and apparatus, which allow induction logging of geological formation through borehole casing.
U.S. Pat. No. 4,820,989 describes methods and apparatus which allow measurement of the resistivity of a geological formation through borehole casing that may be surrounded by brine saturated cement.
U.S. Pat. No. 4,882,542 describes methods and apparatus for measuring electronic properties of geological formations and cement layers adjacent to cased boreholes, including resistivities, polarization phenomena and dielectric constants.
U.S. Pat. No. 4,897,605 describes a well logging system and method that determines the dielectric constant and/or conductivity of earth formations some of which have fluid invasion.
U.S. Pat. No. 4,899,112 describes well logging techniques and apparatus for determining formation resistivity at different radial depths of investigation for determining the existence, locations and properties of beds and caves, and for determining changes in the size of a borehole.
U.S. Pat. No. 4,901,023 describes methods and apparatus for the measurement of the longitudinal components of low frequency A.C. magnetic fields from within cased boreholes, which are used to measure the geophysical properties of geological formations.
U.S. Pat. No. 4,933,638 describes borehole NMR logging apparatus and methods and methods for the interpretation thereof.
U.S. Pat. No. 4,933,640 describes a method and apparatus for determining the distance and direction of a well from a borehole.
U.S. Pat. No. 4,947,119 describes several magnetic resonance imaging methods using adiabatic excitation.
U.S. Pat. No. 5,014,006 describes a device for measuring a weak magnetic field.
U.S. Pat. No. 5,038,107 describes a method and apparatus for making high resolution induction measurements through borehole casing by magnetically saturating the casing.
U.S. Pat. Nos. 5,043,668 and 5,043,669 describe methods and apparatus for measuring electronic properties of geological formations and cement layers adjacent to cased boreholes that includes resistivities, polarization phenomena and dielectric constants.
U.S. Pat. Nos. 5,055,787 and 5,055,788 describe borehole NMR logging apparatus and methods and methods for the interpretation thereof.
U.S. Pat. No. 5,065,100 describes a method for the measurement of the longitudinal components of low frequency A.C. magnetic fields from within cased boreholes that are used to measure the geophysical properties of geological formations.
U.S. Pat. No. 5,136,453 describes a method for suppressing geomagnetically induced currents.
U.S. Pat. No. 5,142,472 describes a method for determining true in-situ resistivity of a thin layer within a formation from dual induction log data.
U.S. Pat. No. 5,159,347 describes microscopic strips of high permeability magnetic conductor that are arrayed in a proximate relation to an electrical conductor to form paths for magnetic circuits about the electrical conductor.
U.S. Pat. No. 5,187,440 describes a method for measuring resistivity changes within a cased well by conducting A.C. current through geological formation separating two cased wells in an oil field undergoing enhanced oil recovery operations such as water flooding operations.
U.S. Pat. No. 5,218,301 describes a method and apparatus for determining the distance from a relief borehole to a target well that utilizes measurements of an electric field at the target well.
U.S. Pat. No. 5,252,918 describes plug released into an oil or gas well that carries one or more metallic strips that affect the inductance of a resistive-inductive bridge circuit mounted adjacent a conduit through which the plug and fluids are pumped into the well.
U.S. Pat. No. 5,260,661 describes a method for the measurement of the longitudinal components of low frequency A.C. magnetic fields from within cased boreholes.
U.S. Pat. No. 5,260,662 describes a method and apparatus that relies on a modified induction approach and that is preferably incorporated into a metal drill collar for MWD measurements.
U.S. Pat. No. 5,313,182 describes a magnet structure for a displacement sensor.
U.S. Pat. No. 5,323,856 describes a system for sensing the passage of a member past a predetermined location along tubing disposed in an oil or gas well.
U.S. Pat. No. 5,359,324 describes a logging-while-drilling system for investigating earth formations.
U.S. Pat. No. 5,426,367 describes a well logging method and apparatus that provides a magnetic saturation signal to at least a transmitter and one receiver mounted in a well casing of a well so as to open xe2x80x9cwindowsxe2x80x9d in the casing to allow the impedances of the formations outside the casing to be logged and recorded and also to detect faults in the casing.
U.S. Pat. No. 5,444,619 describes a system and method for predicting oil reservoir properties throughout the reservoir using well data and seismic data.
U.S. Pat. No. 5,453,693 describes a system for measuring dielectric properties of fluids in an oil well, that utilizes the well casing as a waveguide for certain electromagnetic signals.
U.S. Pat. No. 5,467,769 describes a magnetic field generating apparatus that has a permanent magnet arrangement for generating a magnetic field in a magnetic field generating space and a yoke arrangement for forming magnetic circuits for generation of the magnetic field together with the permanent magnet arrangement.
U.S. Pat. No. 5,495,169 describes a clamp-on magnetic sensor that includes a U-bar first magnetic core section and a straight magnetic core section that integrally fit together so that the straight magnetic core section is held in place by the U-bar.
U.S. Pat. No. 5,497,321 describes a logging tool that provides a log of fractional flow characteristics of formations surrounding an earth borehole.
U.S. Pat. No. 5,498,960 describes a lithology-independent method of well logging the gas saturation in a reservoir containing natural gas.
U.S. Pat. No. 5,510,712 describes a method of determining the resistivity of an underground formation surrounding a cased borehole.
U.S. Pat. No. 5,563,514 describes a method of determining the resistivity of a geological formation through which a metal-cased borehole passes, by means of at least three electrodes in contact with the casing and spaced apart in the longitudinal direction of the borehole.
U.S. Pat. No. 5,570,024 describes methods for determining resistivity of a formation adjacent to a borehole having a casing that uses multiple electrodes and with resistances defined between the electrodes.
U.S. Pat. No. 5,557,200 describes a system for using magnetic resonance techniques to obtain information relating to geologic structures.
U.S. Pat. No. 5,589,775 describes a method for determining the distance and direction from a first borehole to a second borehole that includes generating an elliptically polarized magnetic field in the region of the first borehole.
U.S. Pat. No. 5,633,590 describes the methods for quantitatively determining the separate amounts of oil and gas in a geological formation adjacent to a cased well using measurements of formation resistivity.
U.S. Pat. No. 5,646,533 describes a device for induction measurement of a medium adjacent to a cylindrical, metallic, magnetic walled well of a well casing that includes at least two magnetic circuits for magnetically saturating the metallic wall.
U.S. Pat. No. 5,650,726 describes an emitter for a system for electromagnetic tomographic measurement.
U.S. Pat. No. 5,652,519 describes methods and apparatus for measuring pollutants contaminating earth formation.
U.S. Pat. No. 5,781,436 describes a method of measuring the conductivity of earth formations penetrated by a wellbore.
U.S. Pat. No. 5,798,679 describes an apparatus and method for bending magnetic flux in a magnetic circuit.
U.S. Pat. No. 5,809,458 describes a method of simulating response of a through casing electrical resistivity well logging instrument to a set of simulated earth formations, cement and casing.
U.S. Pat. No. 5,814,988 describes an apparatus for measuring induction resistivity and nuclear magnetic resonance properties of earth formations penetrated by a wellbore.
U.S. Pat. No. 5,825,188 describes an electromagnetic method that can be used to map, track, and monitor subsurface water or solutions and related geologic structure.
U.S. Pat. No. 5,831,433 describes a method for determining a nuclear magnetic resonance characteristic and the resistivity of earth formations surrounding a borehole
U.S. Pat. No. 5,841,281 describes a method of determining the conductivity of earth formations penetrated by a wellbore.
U.S. Pat. No. 5,859,533 describes an emitter for a system of electromagnetic tomographic measurements.
U.S. Pat. No. 5,892,362 describes a method and apparatus for using service induction techniques to produce two-dimensional spatially continuous imaging of subsurface conditions for interpreting and verifying three-dimensional, spatially continuous imaging of subsurface conditions.
U.S. Pat. No. 5,900,733 describes a well logging method and apparatus for determining borehole corrected formation resistivity, borehole diameter, and downhole borehole fluid resistivity.
It is desirable to provide a system and method for measuring the electrical and magnetic characteristics of geologic formations outside a case well from the inside of the case well using magnetic fields. It is especially desirable to provide such a system and method that provides improved information quality by measuring the characteristics at high frequencies. Moreover, it is desirable to use magnetic circuits to direct and control the flow of magnetic flux in magnetic materials to detectors to measure the magnet field through ferromagnetic materials that compose a well casing and to thereby determine the properties of materials outside the well casing beyond the ferromagnetic materials.
Accordingly, it is the primary object of this invention to provide a method and system for measuring the properties of geologic formations outside a case well from inside the case well using magnetic fields.
Another object of this invention is to provide a method and system for logging a well, after its production has diminished or has ended, in order to determine if any other strata or formation at another depth may have missed oil or gas.
A further object of this invention is to provide a method and system for measuring the properties of geologic formations by using magnetic circuits to tap a portion of the magnetic flux flowing in the well casing.
A still further object of this invention is to provide a method and system for measuring the properties of geologic formations that creates a magnetic short circuit by making magnetic contact with a well casing using high permeability ferromagnetic materials.
It is another object of this invention to provide a method and system for measuring the properties of geologic formations by using a magnetic short to channel a portion of magnetic flux through a high permeable material to a magnetic flux detector.
Additional objects, advantages and other novel features of this invention will be set forth in part in the description that follows and in part will be apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of this invention may be realized and attained by means of the instrumentalties and combinations particularly pointed out in the appended claims. Still other objects of the present invention will become readily apparent to those skilled in the art from the following description wherein there is shown and described the preferred embodiment of this invention, simply by way of illustration of one of the modes best suited to carry out this invention. As it will be realized, this invention is capable of other different embodiments, and its several details and specific circuits are capable of modification in various aspects without departing from the invention. Accordingly, the drawings and descriptions that follow should be regarded as illustrative in nature and not as restrictive.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, a magnetic circuit is provided which employs a pipe with a high permeable shunt, a magnetic flux detector, and an electric current generator.